--- a/plugins/mod_register.lua	Wed Dec 23 08:58:34 2015 +0100
+++ b/plugins/mod_register.lua	Wed Dec 23 09:00:03 2015 +0100
@@ -180,8 +180,14 @@
 local throttle_max = module:get_option_number("registration_throttle_max", min_seconds_between_registrations and 1);
 local throttle_period = module:get_option_number("registration_throttle_period", min_seconds_between_registrations);
 local throttle_cache_size = module:get_option_number("registration_throttle_cache_size", 100);
+local blacklist_overflow = module_get_option_boolean("blacklist_on_registration_throttle_overload", false);
 
-local throttle_cache = new_cache(throttle_cache_size);
+local throttle_cache = new_cache(throttle_cache_size, blacklist_overflow and function (ip, throttle)
+	if not throttle:peek() then
+		module:log("info", "Adding ip %s to registration blacklist", ip);
+		blacklisted_ips[ip] = true;
+	end
+end);
 
 local function check_throttle(ip)
 	if not throttle_max then return true end